Untargeted metabolomic reveals the changes in muscle metabolites of mice during exercise recovery and the mechanisms of whey protein and whey protein hydrolysate in promoting muscle repair

Our previous study indicated that whey protein hydrolysate (WPH) showed effective anti-fatigue properties, but its regulatory mechanism on recovery from exercise in mice is unclear. In the present study, we divided the mice into control, WP, and WPH groups and allowed them to rest for 1 h and 24 h after exercise, respectively. The changes in muscle metabolites of mice in the recovery period were investigated using metabolomics techniques. The results showed that the WPH group significantly up-regulated 94 muscle metabolites within 1 h of rest, which was 1.96 and 2.61 times more than the control and WP groups, respectively. In detail, significant decreases in TCA cycle intermediates, lipid metabolites, and carbohydrate metabolites were observed in the control group during exercise recovery. In contrast, administration with WP and WPH enriched more amino acid metabolites within 1 h of rest, which might provide a more comprehensive metabolic environment for muscle repair. Moreover, the WPH group remarkably stimulated the enhancement of lipid, carbohydrate, and vitamin metabolites in the recovery period which might provide raw materials and energy for anabolic reactions. The result of the western blot further demonstrated that WPH could promote muscle repair via activating the Sestrin2/Akt/mTOR/S6K signaling pathway within 1 h of rest. These findings deepen our understanding of the regulatory mechanisms by WPH to promote muscle recovery and may serve as a reference for comprehensive assessments of protein supplements on exercise.

Engineering large and geometrically controlled vascularized nerve tissue in collagen hydrogels to restore large-sized volumetric muscle loss

Developing scalable vascularized and innervated tissue is a critical challenge for the successful clinical application of tissue-engineered constructs. Collagen hydrogels are extensively utilized in cell-mediated vascular network formation because of their naturally excellent biological properties. However, the substantial increase in hydrogel contraction induced by populated cells limits their long-term use. Previous studies attempted to mitigate this issue by concentrating collagen pre-polymer solutions or synthesizing covalently crosslinked collagen hydrogels. However, these methods only partially reduce hydrogel contraction while hindering blood vessel formation within the hydrogels. To address this challenge, we introduced additional support in the form of a supportive spacer to counteract the contraction forces of populated cells and prevent hydrogel contraction. This approach was found to promote cell spreading, resist hydrogel contraction, control hydrogel/tissue geometry, and even facilitate the engineering of functional blood vessels and host nerve growth in just one week. Subsequently, implanting these engineered tissues into muscle defect sites resulted in timely anastomosis with the host vasculature, leading to enhanced myogenesis, increased muscle innervation, and the restoration of injured muscle functionality. Overall, this innovative strategy expands the applicability of collagen hydrogels in fabricating large vascularized nerve tissue constructs for repairing volumetric muscle loss (∼63 %) and restoring muscle function.

The pattern of collagen production may contribute to the gluteal muscle contracture pathogenic process

INTRODUCTION

Arthroscopic release is now the gold standard globally for gluteal muscle contracture (GMC) treatment. However, some patients fail to improve after the first operation and are forced to undergo a second operation. This study explores the essential role collagen fibers may play in muscle contracture in GMC.

METHODS

From February 2010 to May 2018, 1041 hips of 543 GMC patients underwent arthroscopic release. Among them, 498 (91.7%) patients had bilateral GMC and were admitted to the retrospective cohort study. Pathological testing and type III collagen testing were used in contracture tissue studies. Single-cell RNA-sequencing analysis was applied to explore the role of fibroblasts in muscle repair.

RESULTS

Compared with GMC II patients, GMC III patients displayed higher clinical symptoms (P < 0.05). Six weeks after the surgery, the patients in GMC II had a lower prominent hip snap rate, higher JOA score, and better hip range of motion (P < 0.05). Compared with normal muscle tissue, contracture-affected tissue tended to have more type III collagen and form shorter fibers. Recurrent GMC patients seemed to have a higher type III collagen ratio (P < 0.05). In contrast to normally repairable muscle defects, fibroblasts in non-repairable defects were shown to downregulate collagen-related pathways at the early and late stages of tissue repair.

DISCUSSION

This study describes the arthroscopic release of GMC. Study findings include the suggestion that the collagen secretion function of fibroblasts and collagen pattern might influence the muscle repair ability and be further involved in the GMC pathogenic process.

Osteopontin May Improve Postinjury Muscle Repair Via Matrix Metalloproteinases And tgf-β Activation in Regular Exercise

Skeletal muscle injuries are commonly observed during sports and trauma. Regular exercise promotes muscle repair; however, the underlying mechanisms require further investigation. In addition to exercise, osteopontin (OPN) contributes to skeletal muscle regeneration and fibrosis following injury. However, whether and how OPN affects matrix proteins to promote post-injury muscle repair remains uncertain. We recruited regular exercise (RE) and sedentary control (SC) groups to determine plasma OPN levels. Additionally, we developed a murine model of muscle contusion injury and compared the extent of damage, inflammatory state, and regeneration-related proteins in OPN knockout (OPN KO) and wild-type (WT) mice. Our results show that regular exercise induced the increase of OPN, matrix metalloproteinases (MMPs), and transforming growth factor-β (TGF-β) expression in plasma. Injured muscle fibers were repaired more slowly in OPN-KO mice than in WT mice. The expression levels of genes and proteins related to muscle regeneration were lower in OPN-KO mice after injury. OPN also promotes fibroblast proliferation, differentiation, and migration. Additionally, OPN upregulates MMP expression by activating TGF-β, which promotes muscle repair. OPN can improve post-injury muscle repair by activating MMPs and TGF-β pathways. It is upregulated by regular exercise. Our study provides a potential target for the treatment of muscle injuries and explains why regular physical exercise is beneficial for muscle repair.

Bioprotective role of platelet-derived microvesicles in hypothermia: Insight into the differential characteristics of peripheral and splenic platelets

BACKGROUND

Most platelets are present in peripheral blood, but some are stored in the spleen. Because the tissue environments of peripheral blood vessels and the spleen are quite distinct, the properties of platelets present in each may also differ. However, no studies have addressed this difference. We previously reported that hypothermia activates splenic platelets, but not peripheral blood platelets, whose biological significance remains unknown. In this study, we focused on platelet-derived microvesicles (PDMVs) and analyzed their biological significance connected to intrasplenic platelet activation during hypothermia.

METHODS

C57Bl/6 mice were placed in an environment of -20 °C, and their rectal temperature was decreased to 15 °C to model hypothermia. Platelets and skeletal muscle tissue were collected and analyzed for their interactions.

RESULTS

Transcriptomic changes between splenic and peripheral platelets were greater in hypothermic mice than in normal mice. Electron microscopy and real-time RT-PCR analysis revealed that platelets activated in the spleen by hypothermia internalized transcripts, encoding tissue repairing proteins, into PDMVs and released them into the plasma. Plasma microvesicles from hypothermic mice promoted wound healing in the mouse myoblast cell line C2C12. Skeletal muscles in hypothermic mice were damaged but recovered within 24 h after rewarming. However, splenectomy delayed recovery from skeletal muscle injury after the mice were rewarmed.

CONCLUSIONS

These results indicate that PDMVs released from activated platelets in the spleen play an important role in the repair of skeletal muscle damaged by hypothermia.

Effects of different protocols of defocused high-power laser on the viability and migration of myoblasts-a comparative in vitro study

The aim of the present study was to analyze for the first time the effect of photobiomodulation therapy (PBMT) using defocused high-power laser (DHPL) in myoblast cell line C2C12 viability and migration and compare them with low-power laser therapy. Cells were divided into 9 groups: Sham irradiation 10% fetal bovine serum (FBS); Sham irradiation 5%FBS; low-power laser 0.1 W; DHPL 810 1 W; DHPL 810 2 W; DHPL 980 1 W; DHPL 980 2 W; DHPL dual 1 W; DHPL dual 2 W. To simulate stress conditions, all groups exposed to irradiation were maintained in DMEM 5% FBS. The impact of therapies on cell viability was assessed through sulforhodamine B assay and on cells migration through scratch assays and time-lapse. Myoblast viability was not modified by PBMT protocols. All PBMT protocols were able to accelerate the scratch closure after 6 and 18 h of the first irradiation (p < 0.001). Also, an increase in migration speed, with a more pronounced effect of DHPL laser using dual-wavelength protocol with 2 W was observed (p < 0.001). In conclusion, the diverse PBMT protocols used in this study accelerated the C2C12 myoblasts migration, with 2-W dual-wavelength outstanding as the most effective protocol tested. Benefits from treating muscle injuries with PBMT appear to be related to its capacity to induce cell migration without notable impact on cell viability.

Virtually "muscling" in pandemic: first virtual European Muscle Conference (September 20-22, 2021)

A report on the first virtual European Muscle Conference.

A myogenic niche with a proper mechanical stress environment improves abdominal wall muscle repair by modulating immunity and preventing fibrosis

Volumetric muscle loss (VML) healing is often complicated by fibrosis, which impairs muscle regeneration and function. Adjusting mechanical stress in the repair environment may modulate immunity and reduce fibrosis. In this study, we aimed to create a biomaterial with suitable tension conditions and bidirectional tissue-inducing abilities to prevent fibrosis thus promote muscle regeneration and induce aponeurosis-like structures to restore muscle force transmission. A protocol was developed to manufacture decellularized muscle aponeurosis (D-MA) patches with an intact extracellular matrix (ECM) and low cytotoxicity. D-MA optimized the mechanical stress distribution in muscle injury sites and decreased the number of proinflammatory macrophages and myofibroblasts, thereby attenuating muscle fibrosis. Muscle and aponeurosis ECM environments had different microstructures and mechanical properties, which specifically enhanced stem cell differentiation into muscle-like cells on muscle ECM and tenocyte-like cells on aponeurosis ECM in vitro. Four weeks after orthotopic implantation, the biphasic muscle-aponeurosis-like tissue was successfully regenerated by the D-MA scaffold. The regenerated muscle fibers in D-MA were more abundant than those in the fibrotic decellularized muscle (D-M) scaffold. D-MA can be used to repair abdominal defects, which significantly improves the repair outcomes. Our results suggest D-MA as a promising material for VML repair.

Skeletal muscle surrogates for the acquisition of muscle repair skills in upper limb surgery

INTRODUCTION

The required fidelity of synthetic materials in surgical simulators to teach tissue handling and repair requirements should be as accurate as possible. There is a poor understanding of the relationship between choice of muscle surrogates and training outcome for trainee surgeons. To address this, the mechanical characteristics of several candidate synthetic muscle surrogates were measured, and their subjective biofidelity was qualitatively assessed by surgeons.

METHODS

Silicone was selected after assessing several material options and 16 silicone-based surrogates were evaluated. Three of the closest samples to muscle (Samples 1.1, 1.2, 1.3) and one with inserted longitudinal fibres (1.2F) were mechanically tested in the following: compression and tension, needle puncture force and suture pull-out in comparison with real muscle. The four samples were evaluated by 17 Plastic and Orthopaedic surgeons to determine their views of the fidelity with regard to the handling properties, needle insertion and ease of suture pull-out.

RESULTS

The mechanical testing showed the surrogates exhibited varying characteristics that matched some of the properties of muscle, though none recreated all the mechanical characteristics of native muscle. Good biofidelity was generally achieved for compression stiffness and needle puncture force, but it was evident that tensile stiff was too low for all samples. The pull-out forces were variable and too low, except for the sample with longitudinal fibres. In the qualitative assessment, the overall median scores for the four surrogate samples were all between 30 and 32 (possible range 9-45), indicating limited differentiation of the samples tested by the surgeons.

CONCLUSIONS

The surrogate materials showed a range of mechanical properties bracketing those of real muscle, thus presenting a suitable combination of candidates for use in simulators to attain the requirements as set out in the learning outcomes of muscle repair. However, despite significant mechanical differences between the samples, all surgeons found the samples to be similar to each other.

Redressing the interactions between stem cells and immune system in tissue regeneration

Skeletal muscle has an extraordinary regenerative capacity reflecting the rapid activation and effective differentiation of muscle stem cells (MuSCs). In the course of muscle regeneration, MuSCs are reprogrammed by immune cells. In turn, MuSCs confer immune cells anti-inflammatory properties to resolve inflammation and facilitate tissue repair. Indeed, MuSCs can exert therapeutic effects on various degenerative and inflammatory disorders based on their immunoregulatory ability, including effects primed by interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). At the molecular level, the tryptophan metabolites, kynurenine or kynurenic acid, produced by indoleamine 2,3-dioxygenase (IDO), augment the expression of TNF-stimulated gene 6 (TSG6) through the activation of the aryl hydrocarbon receptor (AHR). In addition, insulin growth factor 2 (IGF2) produced by MuSCs can endow maturing macrophages oxidative phosphorylation (OXPHOS)-dependent anti-inflammatory functions. Herein, we summarize the current understanding of the immunomodulatory characteristics of MuSCs and the issues related to their potential applications in pathological conditions, including COVID-19.

Endogenous Galectin-3 is required for skeletal muscle repair

Skeletal muscle has the intrinsic ability to self-repair through a multifactorial process, but many aspects of its cellular and molecular mechanisms are not fully understood. There is increasing evidence that some members of the mammalian β-galactoside-binding protein family (galectins) are involved in the muscular repair process (MRP), including galectin-3 (Gal-3). However, there are many questions about the role of this protein on muscle self-repair. Here, we demonstrate that endogenous Gal-3 is required for: i) muscle repair in vivo using a chloride-barium myolesion mouse model, and ii) mouse primary myoblasts myogenic programming. Injured muscle from Gal-3 knockout mice (GAL3KO) showed persistent inflammation associated with compromised muscle repair and the formation of fibrotic tissue on the lesion site. In GAL3KO mice, osteopontin expression remained high even after 7 and 14 days of the myolesion, while MyoD and myogenin had decreased their expression. In GAL3KO mouse primary myoblast cell culture, Pax7 detection seems to sustain even when cells are stimulated to differentiation and MyoD expression is drastically reduced. The detection and temporal expression levels of these transcriptional factors appear to be altered in Gal-3-deficient myoblast. Gal-3 expression in WT states, both in vivo and in vitro, in sarcoplasm/cytoplasm and myonuclei; as differentiation proceeds, Gal-3 expression is drastically reduced, and its location is confined to the sarcolemma/plasma cell membrane. We also observed a change in the temporal-spatial profile of Gal-3 expression and muscle transcription factors levels during the myolesion. Overall, these results demonstrate that endogenous Gal-3 is required for the skeletal muscle repair process.

Do Interactions of Vitamin D3 and BMP Signaling Hold Implications in the Pathogenesis of Fibrodysplasia Ossificans Progressiva?

PURPOSE OF REVIEW

Fibrodysplasia ossificans progressiva (FOP) is a debilitating rare disease known for episodic endochondral heterotopic ossification (HO) caused by gain-of-function mutations in ACVR1/ALK2. However, disease severity varies among patients with identical mutations suggesting disease-modifying factors, including diet, may have therapeutic implications. The roles of vitamin D₃ in calcium metabolism and chondrogenesis are known, but its effects on BMP signaling and chondrogenesis are less studied. This review attempts to assess the possibility of vitamin D's effects in FOP by exploring relevant intersections of VD₃ with mechanisms of FOP flares.

RECENT FINDINGS

In vitro and in vivo studies suggest vitamin D suppresses inflammation, while clinical studies suggest that vitamin D₃ protects against arteriosclerosis and inversely correlates with non-genetic intramuscular HO. However, the enhancement of chondrogenesis, BMP signaling, and possibly Activin A expression by vitamin D may be more relevant in FOP. There appears to be little potential for vitamin D to reduce HO in FOP, but testing the potential for excess vitamin D to promote HO may be warranted.

Kinin-B2 Receptor Activity in Skeletal Muscle Regeneration and Myoblast Differentiation

The bioactive peptide bradykinin obtained from cleavage of precursor kininogens activates the kinin-B2 receptor functioning in induction of inflammation and vasodilatation. In addition, bradykinin participates in kidney and cardiovascular development and neuronal and muscle differentiation. Here we show that kinin-B2 receptors are expressed throughout differentiation of murine C2C12 myoblasts into myotubes. An autocrine loop between receptor activation and bradykinin secretion is suggested, since bradykinin secretion is significantly reduced in the presence of the kinin-B2 receptor antagonist HOE-140 during differentiation. Expression of skeletal muscle markers and regenerative capacity were decreased after pharmacological inhibition or genetic ablation of the B2 receptor, while its antagonism increased the number of myoblasts in culture. In summary, the present work reveals to date no functions described for the B2 receptor in muscle regeneration due to the control of proliferation and differentiation of muscle precursor cells.

The omentum harbors unique conditions in the peritoneal cavity to promote healing and regeneration for diaphragm muscle repair in mdx mice

Although the primary cause of Duchenne muscular dystrophy (DMD) is a genetic mutation, the inflammatory response contributes directly to severity and exacerbation of the diaphragm muscle pathology. The omentum is a lymphoid organ with unique structural and immune functions serving as a sanctuary of hematopoietic and mesenchymal progenitors that coordinate immune responses in the peritoneal cavity. Upon activation, these progenitors expand and the organ produces large amounts of growth factors orchestrating tissue regeneration. The omentum of mdx mouse, a DMD murine model, is rich in milky spots and produces growth factors that promote diaphragm muscle regeneration. The present review summarizes the current knowledge of the omentum as an important immunologic structure and highlights its contribution to resolution of dystrophic muscle injury by providing an adequate environment for muscle regeneration, thus being a potential site for therapeutic interventions in DMD.

Regeneration competent satellite cell niches in rat engineered skeletal muscle

Satellite cells reside in defined niches and are activated upon skeletal muscle injury to facilitate regeneration. Mechanistic studies of skeletal muscle regeneration are hampered by the inability to faithfully simulate satellite cell biology in vitro. We sought to overcome this limitation by developing tissue engineered skeletal muscle (ESM) with (1) satellite cell niches and (2) the capacity to regenerate after injury. ESMs contained quiescent Pax7-positive satellite cells in morphologically defined niches. Satellite cells could be activated to repair (i) cardiotoxin and (ii) mechanical crush injuries. Activation of the Wnt-pathway was essential for muscle regeneration. Finally, muscle progenitors from the engineered niche developed de novo ESM in vitro and regenerated skeletal muscle after cardiotoxin-induced injury in vivo. We conclude that ESM with functional progenitor niches reminiscent of the in vivo satellite cell niches can be engineered in vitro. ESM may ultimately be exploited in disease modeling, drug screening, or muscle regeneration.

The FRiND Model: A Mathematical Model for Representing Macrophage Plasticity in Muscular Dystrophy Pathogenesis

Muscular dystrophy describes generalized progressive muscular weakness due to the wasting of muscle fibers. The progression of the disease is affected by known immunological and mechanical factors, and possibly other unknown mechanisms. This article introduces a new mathematical model, the FRiND model, to further elucidate these known immunological actions. We will perform stability and sensitivity analyses on this model. The models time course results will be verified by biological studies in the literature. This model could be the foundation for further understanding of immunological muscle repair.

A novel in vitro model for the assessment of postnatal myonuclear accretion

BACKGROUND

Due to the post-mitotic nature of myonuclei, postnatal myogenesis is essential for skeletal muscle growth, repair, and regeneration. This process is facilitated by satellite cells through proliferation, differentiation, and subsequent fusion with a pre-existing muscle fiber (i.e., myonuclear accretion). Current knowledge of myogenesis is primarily based on the in vitro formation of syncytia from myoblasts, which represents aspects of developmental myogenesis, but may incompletely portray postnatal myogenesis. Therefore, we aimed to develop an in vitro model that better reflects postnatal myogenesis, to study the cell intrinsic and extrinsic processes and signaling involved in the regulation of postnatal myogenesis.

METHODS

Proliferating C2C12 myoblasts were trypsinized and co-cultured for 3 days with 5 days differentiated C2C12 myotubes. Postnatal myonuclear accretion was visually assessed by live cell time-lapse imaging and cell tracing by cell labeling with Vybrant® DiD and DiO. Furthermore, a Cre/LoxP-based cell system was developed to semi-quantitatively assess in vitro postnatal myonuclear accretion by the conditional expression of luciferase upon myoblast-myotube fusion. Luciferase activity was assessed luminometrically and corrected for total protein content.

RESULTS

Live cell time-lapse imaging, staining-based cell tracing, and recombination-dependent luciferase activity, showed the occurrence of postnatal myonuclear accretion in vitro. Treatment of co-cultures with the myogenic factor IGF-I (p < 0.001) and the cytokines IL-13 (p < 0.05) and IL-4 (p < 0.001) increased postnatal myonuclear accretion, while the myogenic inhibitors cytochalasin D (p < 0.001), myostatin (p < 0.05), and TNFα (p < 0.001) decreased postnatal myonuclear accretion. Furthermore, postnatal myonuclear accretion was increased upon recovery from electrical pulse stimulation-induced fiber damage (p < 0.001) and LY29004-induced atrophy (p < 0.001). Moreover, cell type-specific siRNA-mediated knockdown of myomaker in myoblasts (p < 0.001), but not in myotubes, decreased postnatal myonuclear accretion.

CONCLUSIONS

We developed a physiologically relevant, sensitive, high-throughput cell system for semi-quantitative assessment of in vitro postnatal myonuclear accretion, which can be used to mimic physiological myogenesis triggers, and can distinguish the cell type-specific roles of signals and responses in the regulation of postnatal myogenesis. As such, this method is suitable for both basal and translational research on the regulation of postnatal myogenesis, and will improve our understanding of muscle pathologies that result from impaired satellite cell number or function.

Volumetric muscle loss injury repair using in situ fibrin gel cast seeded with muscle-derived stem cells (MDSCs)

Volumetric muscle defect, caused by trauma or combat injuries, is a major health concern leading to severe morbidity. It is characterized by partial or full thickness loss of muscle and its bio-scaffold, resulting in extensive fibrosis and scar formation. Therefore, the ideal therapeutic option is to use stem cells combined with bio-scaffolds to restore muscle. For this purpose, muscle-derived stem cells (MDSCs) are a great candidate due to their unique multi-lineage differentiation potential.

In this study, we evaluated the regeneration potential of MDSCs for muscle loss repair using a novel in situ fibrin gel casting. Muscle defect was created by a partial thickness wedge resection in the tibialis anterior (TA)muscles of NSG mice which created an average of 25% mass loss. If untreated, this defect leads to severe muscle fibrosis. Next, MDSCs were delivered using a novel in situ fibrin gel casting method.

Our results demonstrated MDSCs are able to engraft and form new myofibers in the defect when casted along with fibrin gel. LacZ labeled MDSCs were able to differentiate efficiently into new myofibers and significantly increase muscle mass. This was also accompanied by significant reduction of fibrotic tissue in the engrafted muscles. Furthermore, transplanted cells also contributed to new vessel formation and satellite cell seeding.

These results confirmed the therapeutic potential of MDSCs and feasibility of direct in situ casting of fibrin/MDSC mixture to repair muscle mass defects.

The Pleckstrin homology like domain family member, TDAG51, is temporally regulated during skeletal muscle regeneration

The capacity for skeletal muscle to repair from daily insults as well as larger injuries is a vital component to maintaining muscle health over our lifetime. Given the importance of skeletal muscle for our physical and metabolic well-being, identifying novel factors mediating the growth and repair of skeletal muscle will thus build our foundational knowledge and help lead to potential therapeutic avenues for muscle wasting disorders. To that end, we investigated the expression of T-cell death associated gene 51 (TDAG51) during skeletal muscle repair and studied the response of TDAG51 deficient (TDAG51^-/-) mice to chemically-induced muscle damage. TDAG51 mRNA and protein expression within uninjured skeletal muscle is almost undetectable but, in response to chemically-induced muscle damage, protein levels increase by 5 days post-injury and remain elevated for up to 10 days of regeneration. To determine the impact of TDAG51 deletion on skeletal muscle form and function, we compared adult male TDAG51^-/- mice with age-matched wild-type (WT) mice. Body and muscle mass were not different between the two groups, however, in situ muscle testing demonstrated a significant reduction in force production both before and after fatiguing contractions in TDAG51^-/- mice. During the early phases of the regenerative process (5 days post-injury), TDAG51^-/- muscles display a significantly larger area of degenerating muscle tissue concomitant with significantly less regenerating area compared to WT (as demonstrated by embryonic myosin heavy chain expression). Despite these early deficits in regeneration, TDAG51^-/- muscles displayed no morphological deficits by 10 days post injury compared to WT mice. Taken together, the data presented herein demonstrate TDAG51 expression to be upregulated in damaged skeletal muscle and its absence attenuates the early phases of muscle regeneration.

Pharmacological Inhibition of PKCθ Counteracts Muscle Disease in a Mouse Model of Duchenne Muscular Dystrophy

Inflammation plays a considerable role in the progression of Duchenne Muscular Dystrophy (DMD), a severe muscle disease caused by a mutation in the dystrophin gene. We previously showed that genetic ablation of Protein Kinase C θ (PKCθ) in mdx, the mouse model of DMD, improves muscle healing and regeneration, preventing massive inflammation. To establish whether pharmacological targeting of PKCθ in DMD can be proposed as a therapeutic option, in this study we treated young mdx mice with the PKCθ inhibitor Compound 20 (C20). We show that C20 treatment led to a significant reduction in muscle damage associated with reduced immune cells infiltration, reduced inflammatory pathways activation, and maintained muscle regeneration. Importantly, C20 treatment is efficient in recovering muscle performance in mdx mice, by preserving muscle integrity. Together, these results provide proof of principle that pharmacological inhibition of PKCθ in DMD can be considered an attractive strategy to modulate immune response and prevent the progression of the disease.

Research in context

Duchenne muscular dystrophy (DMD) is a severe muscle disease affecting 1:3500 male births. DMD is caused by a mutation in dystrophin gene, coding for a protein required for skeletal and cardiac muscle integrity. Lack of a functional dystrophin is primarily responsible for the muscle eccentric contraction-induced muscle damage, observed in dystrophic muscle. However, inflammation plays a considerable role in the progression of DMD. Glucocorticoids, which have anti-inflammatory properties, are being used to treat DMD with some success; however, long term treatment with these drugs induces muscle atrophy and wasting, outweighing their benefit. The identification of specific targets for anti-inflammatory therapies is one of the ongoing therapeutic options. Although blunting inflammation would not be a “cure” for the disease, the emerging clue is that multiple strategies, addressing different aspects of the pathology, which may eventually converge, may be successful. In this context, we previously showed that genetic ablation of Protein Kinase C θ (PKCθ), an enzyme known to be involved in immune response, in mdx, the mouse model of DMD, improves muscle healing and regeneration, preventing massive inflammation. To establish whether pharmacological targeting of PKCθ in DMD can be proposed as a therapeutic option, in this study we treated young mdx mice with the PKCθ inhibitor Compound 20 (C20). We show that C20 treatment led to a significant reduction in muscle damage associated with reduced immune cells infiltration, reduced inflammatory pathways activation, and maintained muscle regeneration. Importantly, C20 treatment is efficient in recovering muscle performance in mdx mice, by preserving muscle integrity. Together, these results provide proof of principle that pharmacological inhibition of PKCθ in DMD can be considered an attractive strategy to modulate immune response and prevent the progression of the disease.

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Immune-cell intrinsic PKCθ activity might play a hitherto unrecognized role of in the development of DMD.

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Mdx dystrophic mice were treated with the PKCθ inhibitor C20.

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C20 treatment prevents damage and inflammation in dystrophic muscle, while improving muscle regeneration.

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C20 treatment prevents drop in force and ameliorates fatigue resistance in dystrophic mice.

Leucine-enriched essential amino acids attenuate inflammation in rat muscle and enhance muscle repair after eccentric contraction

Eccentric exercise results in prolonged muscle damage that may lead to muscle dysfunction. Although inflammation is essential to recover from muscle damage, excessive inflammation may also induce secondary damage, and should thus be suppressed. In this study, we investigated the effect of leucine-enriched essential amino acids on muscle inflammation and recovery after eccentric contraction. These amino acids are known to stimulate muscle protein synthesis via mammalian target of rapamycin (mTOR), which, is also considered to alleviate inflammation. Five sets of 10 eccentric contractions were induced by electrical stimulation in the tibialis anterior muscle of male SpragueDawley rats (8–9 weeks old) under anesthesia. Animals received a 1 g/kg dose of a mixture containing 40 % leucine and 60 % other essential amino acids or distilled water once a day throughout the experiment. Muscle dysfunction was assessed based on isometric dorsiflexion torque, while inflammation was evaluated by histochemistry. Gene expression of inflammatory cytokines and myogenic regulatory factors was also measured. We found that leucine-enriched essential amino acids restored full muscle function within 14 days, at which point rats treated with distilled water had not fully recovered. Indeed, muscle function was stronger 3 days after eccentric contraction in rats treated with amino acids than in those treated with distilled water. The amino acid mix also alleviated expression of interleukin-6 and impeded infiltration of inflammatory cells into muscle, but did not suppress expression of myogenic regulatory factors. These results suggest that leucine-enriched amino acids accelerate recovery from muscle damage by preventing excessive inflammation.

GRAF1 deficiency blunts sarcolemmal injury repair and exacerbates cardiac and skeletal muscle pathology in dystrophin-deficient mice

Background

The plasma membranes of striated muscle cells are particularly susceptible to rupture as they endure significant mechanical stress and strain during muscle contraction, and studies have shown that defects in membrane repair can contribute to the progression of muscular dystrophy. The synaptotagmin-related protein, dysferlin, has been implicated in mediating rapid membrane repair through its ability to direct intracellular vesicles to sites of membrane injury. However, further work is required to identify the precise molecular mechanisms that govern dysferlin targeting and membrane repair. We previously showed that the bin–amphiphysin–Rvs (BAR)–pleckstrin homology (PH) domain containing Rho-GAP GTPase regulator associated with focal adhesion kinase-1 (GRAF1) was dynamically recruited to the tips of fusing myoblasts wherein it promoted membrane merging by facilitating ferlin-dependent capturing of intracellular vesicles. Because acute membrane repair responses involve similar vesicle trafficking complexes/events and because our prior studies in GRAF1-deficient tadpoles revealed a putative role for GRAF1 in maintaining muscle membrane integrity, we postulated that GRAF1 might also play an important role in facilitating dysferlin-dependent plasma membrane repair.

Methods

We used an in vitro laser-injury model to test whether GRAF1 was necessary for efficient muscle membrane repair. We also generated dystrophin/GRAF1 doubledeficient mice by breeding mdx mice with GRAF1 hypomorphic mice. Evans blue dye uptake and extensive morphometric analyses were used to assess sarcolemmal integrity and related pathologies in cardiac and skeletal muscles isolated from these mice.

Results

Herein, we show that GRAF1 is dynamically recruited to damaged skeletal and cardiac muscle plasma membranes and that GRAF1-depleted muscle cells have reduced membrane healing abilities. Moreover, we show that dystrophin depletion exacerbated muscle damage in GRAF1-deficient mice and that mice with dystrophin/GRAF1 double deficiency phenocopied the severe muscle pathologies observed in dystrophin/dysferlin-double null mice. Consistent with a model that GRAF1 facilitates dysferlin-dependent membrane patching, we found that GRAF1 associates with and regulates plasma membrane deposition of dysferlin.

Conclusions

Overall, our work indicates that GRAF1 facilitates dysferlin-dependent membrane repair following acute muscle injury. These findings indicate that GRAF1 might play a role in the phenotypic variation and pathological progression of cardiac and skeletal muscle degeneration in muscular dystrophy patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13395-015-0054-6) contains supplementary material, which is available to authorized users.

Thyroid Hormone Signaling in Muscle Development, Repair and Metabolism

Skeletal muscle is a plastic organ made by highly specialize fibers with specific and different structure, function and metabolism. Skeletal muscle fibers can adapt, change, recover/regenerate after injury in response to various stimulators including hormones. Thyroid hormones are important players in the homeostasis of several tissue including skeletal muscle and their genomic action mostly depend on the tissue T3 bioavailability and on the distribution of the thyroid receptor isoforms which act as transcription factors and are modulated by T3. Changing in contractile and metabolic proprieties of the muscle fibers has been described in experimental models of hyper and hypothyroidism. Animal models with disruption of thyroid hormone signaling showed different and specific skeletal muscle phenotypes. By focusing on thyroid hormone signaling in skeletal muscle homeostasis, we review T3 specific action on skeletal muscle development, postnatal growth, function and metabolism.